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8 Oct 2017, 3 significant Earthquakes

  1. Oct 8, 2017 #1

    davenn

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    3 respectable events within 10 hours

    M 6.1 - 153km NW of Pangai, Tonga

    M 6.3 - Balleny Islands region

    M 6.6 - 60km E of Buldir Island, Alaska

    171008 M 6.1 Tonga, 6.3 Balleny Is, 6.6 Aleutians zhi.gif


    The first 2 events are on this map. The third event, the M 6.6 in the western Aleutian Islands, is the other end of the pacific from me.

    171008  M6.1 Tonga, M6.3 Balleny Is.JPG


    The largest event, the M6.6 is the smallest on the seismogram
    1) it was the furthest from me and
    2) it was reasonably deep, ~ 111 km, so Surface waves were low level


    Dave
     
  2. jcsd
  3. Oct 8, 2017 #2

    fresh_42

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    I've heard or read somewhere that you live on the fastest moving ship of all.
     
  4. Oct 8, 2017 #3

    davenn

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    ummm please clarify :smile:
     
  5. Oct 8, 2017 #4

    fresh_42

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    This is a bit embarrassing because I have no scientific source. It had been said that the Australian plate is the fastest moving one (towards north).
     
  6. Oct 8, 2017 #5

    davenn

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    ohhh OK, I was wondering if you were referring to something like that but wasn't sure :smile:

    The Indo-Australian plate isn't the fastest moving one but it is still at a reasonable speed, there is a notable difference
    between the western part of the plate and the eastern part

    from Australian Science ......

    For the high speeds look to the Tonga - Kermadec Trench where the Pacific seafloor is diving down under the edge
    of the Indo-Australian Plate at up to 7.5 cm / yr
    That trench basically covers the region from offshore eastern North Is., NZ up to around the Tonga/Samoa region.
    This results in regular large and often very deep earthquakes


    Dave
     
    Last edited: Oct 9, 2017
  7. Oct 9, 2017 #6
    In the last few years, I read that earthquakes generate frequencies which allow 'remote triggering' in faults that respond to the same frequency. More properly, the same spectrum of frequencies. If the travel time for the seismic waves is appropriate, could one of these be a case of remote triggering?

    More importantly, are sensitivity frequencies are being compiled for the major faults. I can hope that, after a powerful earthquake, the spectrum of frequencies will prompt a warning to the civil authorities where populations are threatens next. Something like the Pacific tidal wave warnings.

    Is this spectral information being compiled?
     
  8. Oct 10, 2017 #7

    jim mcnamara

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    @MRBlizzard
    It helps us enormously when 'I read somewhere' is presented something like I read an article 'XXXX YYYY' in Science Magazine. The reason for this is a lot of what 'I read' may really not be good science, but somebody's speculation or non-standard interpretation. So it leads to:

    I'll guess something from a good source: http://www.jstor.org/stable/2881709?seq=1#page_scan_tab_contents

    This does not mention harmonics at all. Just large non-linear dyanamic strain. So where do we go from here? I may have guessed wrong. You may have mis-remembered. Nobody knows.

    The point is that vague references can lead to awful answers. Please help us here. We need all the help we can get.
    Thanks.
     
  9. Oct 10, 2017 #8

    davenn

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    Thanks Jim :smile:


    I have never heard of that. I don't think fault lines can have specific frequencies, or a spectrum thereof.

    As Jim said ... you need to cite references, maybe 1) they are bad info, 2) you misunderstood what was being said ??


    see my above comments


    The only thing I can say is that large events do sometimes trigger events elsewhere but the documented cases are few and far between

    The only one that comes to mind is the 1992, M7.3, Landers ( Southern California) that was deemed to have triggered events in Northern California and also possibly the M6.5 Big Bear event in Southern California

    https://www.researchgate.net/public...ke_at_Long_Valley_Volcanic_Caldera_California

    https://broom02.revolvy.com/topic/Landers, California earthquake&item_type=topic



    cheers
    Dave
     
  10. Oct 10, 2017 #9

    mfb

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    There are about 160 M6+ earthquakes per year (average of the last 10 years). For a random uniform distribution, the probability that two of them occur within 12 hours of a given other one is 2%. On average we expect this to happen 3 times per year by chance. Roughly every 5 years we expect 4 uncorrelated M6+ earthquakes to happen within 12 hours. This does not include aftershocks, which are clearly correlated.
     
  11. Oct 10, 2017 #10
    Please support that
    (seems a bit arbitrary)
     
  12. Oct 10, 2017 #11

    mfb

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    For uncorrelated events the number of earthquakes in a 12 hour window follows a Poisson distribution with a mean of 160*12h/(1 year) = 0.219.
    Poisson(0.219,2)=0.019, as we have 160 "attempts" per year we expect 160*0.019=3.0 such events per year.
    Poisson(0.219,3)=0.0015, we expect this once every 1/(160*0.0015)=4.2 years. As I didn't use a calculator for the last number I made a rough estimate.

    Note: The calculation for 3 events neglects the probability for 4 events close together (as it would give two sequences of 3 events), and similar for 4 and 5, but as there is a factor 10 between them that is a good estimate and the error is very small.
     
  13. Oct 10, 2017 #12
    Interesting! You have my respect!
     
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